In pressure gas-respirators with excess pressure in the oxygen mask, it must be made sure that there is an excess pressure in the oxygen mask during its use, both in the exhaling and in the inhaling phase. This excess pressure prevents, under any circumstances, penetration of the surrounding atmosphere into the oxygen mask during its use, which could be hazardous. Possible leaks always cause a gas flow from the inside to the outside of the mask.
All known apparatus, however have the great disadvantage that the breathing gas-storage tanks are closed at the end of the use and with the removal of the oxygen mask; hence the opening of the breathing cycle, or the operation of the lung machine must be switched, otherwise the breathing gas would flow out of tank and thus shorten the time of use.
A known lung-controlled compressed air-respirator with excess pressure in the oxygen mask has a lung-controlled valve whose shutter is moved by operation of a tipping lever by a control diaphragm admitted from the outside with recirculated air and from the inside with pressure inside the mask. The movement of the control diaphragm can be limited by a distance bolt moving in longitudinal directions from the control space to the outside. The distance bolt is loaded by a compression spring and is to this end held in an eccentric lever in such a way relative the control diaphragm that it:
(a) keeps the control diaphragm in a closed position in which the valve is closed by the tipping lever; but
(b) permits full movement of the control diaphragm in the other excess pressure position.
In a locked position (a), in which the eccentric lever points upwardly and the valve is closed, no breathing gas escapes unnecessarily, even when the oxygen mask is removed, or in the case of great leaks. In an excess pressure position (b) with the eccentric bolt pointing downwardly, breathing gas flows, and the desired excess pressure builds up in the oxygen mask.
The excess pressure position (b) is gradually switched-in again from the locked position (a), when the oxygen mask is attached and, with a deep breath of the user, by automatic downward rotation of the eccentric lever.
A disadvantage remains however in that when the oxygen mask is removed, the eccentric lever must be turned by hand from excess pressure position (b) into locked position (a). If this is not done, breathing gas will be lost (DOS No. 26 20 170).
The following known circulating air respirator with excess pressure in the oxygen mask likewise requires a manual act to avoid unnecessary breathing gas losses.
In this apparatus the breathing gas flows to the apparatus carrier from a breathing bag over an inhaling hose with an inhaling valve just in front of the oxygen mask. The exhaled gas arrives over an exhaling valve in the exhaling hose and flows through the latter and a CO.sub.2 absorber back into the breathing bag. In order to produce the excess pressure the breathing bag is loaded from the outside with a spring.
In order to cover oxygen consumption, oxygen is supplied continuously to the breathing bag, and additionally through an emergency valve over a pressure reducer from an oxygen cylinder. The emergency valve is controlled by the movement of the breathing bag resulting from the movement of the breathing gas. It opens with the collapse of the breathing bag and closes again with its inflation.
Before the oxygen mask is removed, the cylinder valve must be closed. Failing to do so will result in a great oxygen loss, because, when the breathing cycle is opened, by the removal of the oxygen mask or by the appearance of a leak, the excess pressure drops in the mask. The breathing bag is thus compressed by the outer spring, and the emergency valve opens. Oxygen can thus flow out (brochure BP-0878, Biomarine Industries, Inc.).